Numerous arrangements have been proposed for providing improved traction in athletic shoes in the direction longitudinally of the shoe to assist during acceleration, such as conventional cleats or spikes. These, however, also resist pivoting about the ball portion of the shoe as well as sliding movement laterally of the shoe.
Other arrangements that have been suggested, such as disclosed in U.S. Pat. No. 3,555,697 and German patent No. 30 09 381, include bristles embedded in the soles of the shoes and inclined generally in one direction so that the bristles tend to dig into the ground as force is applied to the shoe--that is, the bristles are inclined toward the rear of the sole to resist rearward movement of the shoe relative to the ground and thus to improve traction for forward movement. The amount of grip between the sole and the ground in such an arrangement depends on the number of bristles provided, as well as on the relative stiffness and length of the bristles. The stiffness of the bristles, however, affects their resistance to sliding relative to the ground in all directions. The length of the bristles affects not only their penetration into the ground but also their bending characteristics which, in turn, affects the useful life of the shoe.
U.S. Pat. No. 4,670,997 to Beekman discloses a shoe having a sole for initially facilitating rotation about an axis of rotation normal to the sole in response to the application of a moment about the axis of rotation. The sole contains flexible members radially spaced from the axis of rotation and guide means for impeding the flexing of the flexible members in response to forces which do not create moments about the axis of rotation so as to improve traction in the direction longitudinally of the shoe. The guide means allows flexing of the flexible members in response to forces which do create moments about the axis of rotation. This initially facilitates rotational motion of the foot relative to the ground. However, the shoe and foot only rotate easily until the flexible members are bent so that their lowermost surfaces are flush with the lowermost surfaces of the guide means. The lowermost surfaces of the guide means have high frictional contact with the ground and will tend to impede further rotation of the shoe and foot. Thus, only a limited range of rotational motion is provided, subjecting the wearer's foot to potentially injurious forces.
Other approaches to improve traction in shoes have included embedding elements in grooves in the soles such as the use of ropelike elements disclosed in U.S. Pat. No. 1,664,728 which are designed to support the side walls of relatively deep groves in the sole and thus to maintain the edges of the grooves in a gripping relation with the ground. Another approach of this nature as disclosed in U.S. Pat. No. 1,829,941 comprises a blade seated in a groove in the heel that protrudes from the surface of the heel to provide traction, for example, on ice. Devices of this nature are not suitable for use on surfaces such as artificial turf.